This invention relates generally, as indicated, to a direct drive valve force motor with gain shaping provision. More particularly, this invention relates to certain improvements in limited angle torque motors generally of the type shown in U.S. Pat. No. 4,510,403, which is incorporated herein by reference, and is assigned to the same assignee as the present application.
Motors of this type are particularly suited for use in certain types of direct drive valve servo actuation systems such as those used to actuate aircraft flight controls and the like. Such systems are required to meet precise and demanding performance characteristics, particularly about the neutral position of the actuator and more particularly about the neutral position of the direct drive valve associated therewith.
An important aspect of such a direct drive valve is its ability to perform well with a relatively low level of hydraulic fluid leakage. High fluid leakage may result in excessive heat generation, increased power requirements, and associated weight and increased operational costs.
More recently, with the advent of very high pressure hydraulic systems of up to 8,000 psi, valve leakage about the neutral position has become a much greater concern in that, for an equivalent metering orifice, valve neutral leakage at 8,000 psi may be two or more times that at 3,000 psi.
One way to reduce valve neutral leakage and associated hydraulic power consumption without compromising performance is to provide a significant amount of valve metering orifice overlap. However, this has the disadvantage that the valve plunger must travel through a greater distance (corresponding to the overlap region) before substantial flow begins.
Another area of concern with such a direct drive valve construction involves the friction related breakout force of the valve plunger about its neutral position. Breakout friction can cause excessive threshold levels, instability, and low amplitude frequency response degradation.